Electrophotographic preparation of color television display tube including rinsing phosphor pattern with solution of antistatic agent in apolar solvent

Abstract

The electrophotographic manufacture of the phosphor patterns for a display screen of a color television display tube. This process is performed in as many stages as there are different phosphor zones and possibly also for a light-absorbing intermediate pattern. Contamination of a phosphor which has already been precipitated may easily occur with a next phosphor in this case. According to the invention this is obviated by an intermediate rinsing operation with a solution of an antistatic agent, in an apolar solvent. The antistatic agent is selected from the group consisting of soaps of bivalent metals, soaps of multivalent metals and mixtures thereof.

What is claimed is: 
     
       1. In the method of electrophotographically manufacturing a display screen for a color television display tube wherein a combustible conducting coating is first applied to the face-plate of said tube, a combustible photo-conducting coating is applied to said combustible coating, a first pattern of phosphor zones is formed on said combustible photo-conducting coating by first uniformly electrically charging said photo-conducting coating, forming a latent charge pattern with the charged portions corresponding to the desired phosphor zones of said first pattern by exposing to light the zones on said electrically charged photoconducting coating between said desired phosphor zones, and then precipitating phosphor particles, having charges opposite to the charge on said unexposed portions of said electrically charged photo-conducting coating, from a suspension thereof in an apolar suspending medium, on said unexposed zones of said light electrically charged photo-conducting coating to thereby form the first pattern of phosphor zones, at least one subsequent pattern of phosphor zones is formed on said first pattern of phosphor zones by proceeding in a manner analogous to the formation of said first pattern of phosphor zones and said face-plate is then heated to remove by combustion said combustible conducting coating and said combustible photo-conducting coating, the improvement wherein after the formation of each phosphor pattern and before the formation of the subsequent charge pattern the resultant screen is wetted with a solution consisting essentially of an antistatic agent in an apolar solvent said antistatic agent being selected from the group consisting of soaps of bivalent metals, soaps of multivalent movalent metals and mixtures of said soaps, the conductivity of which soaps in said apolar solvent is between 5×10 -12  and 10 -10  ohm -1  cm -1  (500-10,000 p S/m) the electrical conductivity of which solvent is less than 10 -4  ohm -1  cm -1  (1 p S/m) and dried. 
     
     
       2. The method of claim 1 wherein the conductivity of the metal soaps in the apolar solvent is between 10 × 10  -12  and 80 × 10  -12  ohm -1  cm -1  (1000 - 8000 s/m. 
     
     
       3. The method of claim 1 wherein a light-absorbing coating is provided between the phosphor particles by applying to the photo-conducting coating bearing the phosphor zones a suspension in an apolar liquid, of light absorbing particles having a charge of the same sign as the phosphor particles. 
     
     
       4. A colour television display tube whose display screen is obtained by a method as claimed in claim 1.